1. Field of the Invention
The present invention generally relates to bypass plunger for oil and gas operations and more particularly to improvements in the structure of such instruments to provide increased utility and operating life.
2. Background of the Invention and Description of the Prior Art
Bypass plungers for reciprocatingly lifting gas and fluids from a low or non-productive oil or gas well are well known in the art and are available in a wide variety of forms and construction. The requirements for constructing a reliable bypass plunger are well-understood and numerous innovations in their design and construction have appeared over the years. However, such plungers are used in a variety of circumstances and environments, giving rise to failures or inefficiencies that suggest a solution for an improved design or construction is needed.
Conventional bypass plungers take many forms, employing a variety of configurations to enable them to restore production to an oil or gas well that has been shut in or has become dormant because of insufficient pressure in the formation to yield profitable production. A typical bypass plunger is formed as a hollow, cylindrical body that has a valve system at its lower end for alternately opening and closing fluid passages through the body of the plunger. When the valve system is open, the plunger is allowed to fall through a well bore as the fluid contained in the well bore flows through the hollow body. When the plunger reaches the bottom of the well bore the valve system closes off the hollow interior of the plunger body so that the plunger forms a piston that may rise upward through the well bore if there is sufficient pressure within the formation to lift the plunger and any fluid or gas above the plunger toward the surface. Upon reaching the surface, a mechanism that functions as a decoupler opens the valve system on the plunger to allow the plunger to once again fall through the well bore. This repetitive reciprocating motion of the plunger thus acts to restore production to the well.
A key mechanism in the bypass plunger is the valve system as used in plungers that use a dart valve system. Attached to the lower end of a typical plunger body may be a hollow extension of the body that includes openings in the side walls of the extension. The extension is called a “cage” because of its hollow structure and the openings formed in its side walls. The openings in the side walls of the valve cage act as ports for the flow of fluids through them when the plunger is descending through the well. The cage forms a fraction of the overall length of the plunger body. Within the cage is a poppet valve having a round valve head attached at its underside to a valve stem. The valve head is a larger diameter portion having a valve face formed on the side of the valve head opposite the stem. The head of the valve is disposed within a chamber inside the plunger body just above the cage. This chamber is shaped to match the shape of the head so that it forms a valve (head) seat. The shaft or valve “stem” of the poppet valve, also called a dart valve that is supported within a cylindrical bore within the valve cage, extends through the open lower end of the cage. The dart valve is allowed to reciprocate within its supporting structure as it alternately moves between a closed (valve head against the internal valve seat in the chamber) and open (valve head disposed away from its seat and the valve stem extending outward below the lower end of the plunger body.
Instead of a valve spring that acts to close the dart valve face against its internal valve seat, a clutch assembly disposed within the supporting structure that surrounds the valve stem is configured to restrain the reciprocating motion of the poppet valve within the valve cage. The clutch grips the dart valve stem with just enough friction to restrain the motion of the valve stem when the plunger is descending or ascending through the well bore. Thus, during descent, the clutch holds the dart valve head away from its valve seat, permitting the fluids in the well to flow through the openings in the side wall of the valve cage. When the plunger reaches the bottom of the well, the outward end of the valve stem extending from the lower end of the valve cage strikes a bumper at the bottom of the well that forces the valve stem to move inward. This action overcomes the grip of the clutch on the stem so that the dart valve head moves against its valve seat to close the valve so that fluids can no longer flow through the valve cage and the plunger body. When pressure in the formation is sufficient, the plunger ascends through the well bore as the clutch holds the dart valve closed. At the surface, a decoupler mechanism acts through the upper end of the hollow plunger body until it strikes the upper end of the valve head. This forces the dart valve head to overcome the grip by the clutch, causing the valve to slide downward to open the valve in preparation for the next descent. The cycle of descent and ascent is allowed to repeat itself as long as the reciprocating “pumping action” of the plunger is needed to restore production.
In conventional bypass plungers and similar devices the clutch portion of a dart valve assembly typically comprises a split bobbin formed of a stainless steel alloy into two identical hemispherical halves. Grooves—usually two—surround the outer diameter of the assembled bobbin halves. A coil spring, which is typically formed from an alloy or stainless steel, is formed into a ring or ‘garter’ and disposed in each groove around the bobbin to clamp the bobbin halves against the valve stem. The tension in the springs is adjusted to exert just the right amount of clamping pressure of the bobbin halves around the stem of the dart valve to hold the stem from moving during descent or ascent within the well bore. While these materials are durable and can be suited to use in these type of clutches, such clutches are often subject to severe impact during use that shortens their useful life. For example, the momentum of the relatively massive metal bobbin subjects it to substantial impact forces and the likelihood of damage and a shorter useful life. The springs are also subject to damage when they move within their respective grooves and strike the metal bobbin with sufficient force to deform the spring, although this effect may be partly countered by the resilience of the springs.
Such impacts as described above cause failures that result in substantial losses of time and production to retrieve the plunger and repair or replace it so that production can resume. Even though made of robust metal alloys, the components of a dart valve assembly are subject to damage due to impacts, wear due to friction, and deterioration due to high temperatures, caustic substances in the well and the like, which weakens the components of the dart valve assembly and its surfaces. These conditions make conventional assemblies less effective and more susceptible to failure.
What is needed is a more rugged dart valve assembly that provides the needed clutch action yet has a longer life and is still easy to manufacture.